The present invention relates to a process for the recovery of molybdenum-99 from a matrix containing neutron irradiated, fissionable materials and fission products, in which the matrix is decomposed in an aqueous alkali hydroxide solution and the molybdenum-99 and part of the fission products are dissolved, the solution containing the molybdenum-99 is separated from a residue of solid particles containing at least actinides and lanthanides and is treated with thiocyanate ions in order to form a molybdenum-99 complex.
In nuclear medicine, the significance of Tc-99 is continuously at an increase as an indicator in the diagnosis of tumors. Since, however, technitium has a relatively short halflife (T.sub.1/2 = 6.0 h), the mother nuclide Mo-99 is eluted when required. Thus, a technitium generator is used to provide the technitium. The technitium generators generally comprise a chromatographic column having Mo-99 bearing molybdate ion absorbed thereon. Radioactive decay of the relatively, long-lived Mo-99 produces Tc-99. Elution of the chromatographic column provides an on-the-spot source of the technitium.
Previously, natural molybdenum which had been activated in reactors was used in the generators to produce the technitium. The drawbacks of this natural molybdenum material are that large columns are required for small specific activities, large injection volumes are required in order to retain the required activity, and there is a very limited availability of the generator due to the low activity.
Fission molybdenum has been found to be useful in technitium generators to produce the technitium and has been used to a greater degree in recent times. This, however, requires much refined processing technology in order to obtain the required degrees of molybdenum purity. The required radionuclide purity of the fission molybdenum for use in a technitium generator is:
.gamma. : I-131 &lt;0.05 .mu.C/mC Mo-99 PA1 .alpha. : no more than 1 nanocurie total PA1 .beta. : Sr-89 &lt; 6 .times. 10.sup.-4 .mu.C/mC Mo-99
Ru-103 &lt;0.05 .mu.C/mC Mo-99 PA2 Total .gamma. contamination &lt;0.1 .mu.C/mC Mo-99 PA2 .alpha. activity per curie Mo-99 PA2 Sr-90 &lt; 6 .times. 10.sup.-5 .mu.C/mC Mo-99
A long known method for proving the presence of molybdenum where the molybdenum is present in solution as molybdate comprises reducing the molybdate with SnCl.sub.2 to Mo(III), then binding the Mo(III) to SCN.sup.- ions to form a thiocyanate complex, and thereafter extracting the thiocyanate complex with the aid of diethyl ether. This method is completely useless in the recovery of Mo-99 because of the great volatility and combustibility of the diethyl ether inasmuch as the risk of a fire of explosion must be completely eliminated when working with radioactive substances.
A number of publications discuss methods which use thiocyanate ions, but these methods operate principally with the use of additional extracting agents in the organic phase, such as, for example, with tributyl phosphate (TBP) (Gorlach, V. F., Marchenko, L. M. (Kiev State University), Ukr. Khim. Zh.; 40: No. 9, 983-985, September, 1974 (in Russian)); or with tribenzylamine (Yatirajam, V., Ram, Jaswant (University of Kurukshetra, India), Anal. Chim. Acta; 59; No. 3, 381-387, May 1972); or with 2-furaldehyde (Spaccamela Marchetti, Elena, Cereti Mazza, Maria Teresa (Politecnico, Turin) Ann. Chim., Rome, 59; 902-911, 1969 (in Italian)). These methods have the drawback that the additional organic extraction agents may lead to contamination of the final product which could result in behavioral malfunctions of the molybdenum on the generators. Furthermore, these contaminants may have a pyrogenic effect.